1. Field of the Invention
The invention generally relates to apparatus which is operable to obtain an indication of the velocity of a vehicle constructed of or containing magnetic material and does so without the need to transmit and receive electromagnetic radiation.
2. Background Information
Various types of electronic devices exist for detecting the velocity of vehicular traffic along a roadway. By way of example, law enforcement agencies utilize handheld or vehicle mounted devices which project radar or optical signals at an on-coming vehicle, the velocity of which may be determined from the return signal reflected from the vehicle.
The physical presence of a law enforcement officer and vehicle may be communicated to on-coming traffic to thereby defeat the purpose of the apparatus. Furthermore, various devices may be purchased by the driving public to detect such signals thus causing the driver to slow down during the brief period that the driver's vehicle is being "illuminated". Finally, police officers have recently voiced concerns that hand-held radar speed measuring devices may cause cancer in the officers using them.
A need exists therefore for apparatus which can measure the velocity of a vehicle without transmitting any electromagnetic energy which may be detected, and which apparatus may be hidden from view. The present invention provides for a passive velocity measuring system which meets these objectives.